What is Flicker-Free Lighting?

What Causes LED Flicker?

LED flicker is caused by variations in the current supplied to the LED array, typically originating from the LED driver. Common causes include:

• Poor driver quality — cheap drivers with inadequate smoothing capacitors allow AC ripple to pass through to the LEDs, causing 100Hz flicker (double the 50Hz mains frequency) • Incompatible dimming — phase-cut (mains) dimming with drivers not designed for it causes visible flicker at low dim levels • Voltage instability — mains supply fluctuations can cause driver output variations

The flicker may be invisible at full output but becomes pronounced at lower dim levels — particularly below 20% — which is precisely when occupants are most sensitive to visual disturbance.

Measuring Flicker: SVM and PstLM

Two standardised metrics are used to quantify flicker:

• PstLM (Short-term flicker severity) — measures the likelihood of visible flicker being perceptible. A PstLM of 1.0 means flicker is perceptible to 50% of observers. BS EN 61547 and IEEE 1789 recommend PstLM < 1.0.

• SVM (Stroboscopic Visibility Measure) — measures the stroboscopic effect, where moving objects appear to jump or freeze under flickering light (similar to a strobe effect). SVM < 0.4 is considered imperceptible. SVM < 0.9 is acceptable under EU Ecodesign regulations (EU 2019/2020).

The EU Ecodesign regulation now mandates SVM < 0.4 and PstLM < 1.0 for all LED products placed on the European market — making flicker compliance a legal requirement.

Specifying Flicker-Free LED Luminaires

To ensure flicker-free performance:

• Specify luminaires with high-quality drivers from reputable manufacturers (Tridonic, Osram, Philips Xitanium, Helvar) • Request PstLM and SVM values on product datasheets — reputable manufacturers publish these • For dimming applications, specify DALI or DALI-2 dimming rather than mains dimming — digital dimming protocols are inherently flicker-free at all dim levels • In healthcare, education and office environments, mandate PstLM < 1.0 and SVM < 0.4

All EOS luminaires are tested for flicker compliance and use specification-grade drivers that deliver flicker-free performance across the full dimming range.